Support multiple forms of inline suppression

[lexidor]

Fixes #308
This PR adds the following default suppressors.
@lint-ignore x, @lint-fixme x, @lint-ignore-all x, HHAST_IGNORE[x].
You may now also specify suppression aliases in hhast-lint.json.

[jjergus]

I have mixed feelings about this...what's the value of having so many different keywords?

The value of having a single keyword is that you can do grep HHAST_IGNORE_ERROR *.hack to find all ignored lints, there's less stuff for people to remember when writing/reading code, etc.

[lexidor]

I think adding HHAST_IGNORE is a good change. HHAST_IGNORE_ERROR suggests the linter away behavior is erroneous. The @lint-* are meant for interoperability with HackAST. This allows Facebook to lint against the hsl directory. I guessed HackAST's syntaxes for global and fixme.

I don't know for sure if the alias feature I implemented matches what Fred had in mind. Should aliases only be able to alias the linter name, whilst still being required to have a HHAST_* or @lint-* prefix? I am starting to second guess supporting // This is a polling loop. It is unclear that it is suppressing a linter and looks like a useless inline comment. Wide use of this might discourage removal of useless inline comments, because they might be suppressing a linter.

[fredemmott]

• HHAST_IGNORE seems like a good change, and has minor change to grepability
• for the others, perhaps it would be best to make it configurable via hhast-lint.json

[lexidor]

Major merge conflict with refactored code base.